A swash-plate type variable-capacity compressor used for air-conditioning systems for automobiles, etc., is equipped with, among others, a rotational shaft that rotates by being driven by the rotational force of the engine, a swash plate connected to the rotational shaft at a variable tilt angle, and a compression piston connected to the swash plate, wherein the tilt angle of the swash plate is changed in order to change the piston stroke and thereby control the discharge rate of the refrigerant gas.
The tilt angle of the swash plate can be changed continuously by adjusting the state of balance between the pressures acting upon both sides of the piston, which is in turn achieved by controlling the pressure in a control chamber as appropriate by using a capacity control valve that utilizes the intake pressure of an intake chamber into which refrigerant gas is taken in, the discharge pressure of a discharge chamber from which piston-pressurized refrigerant gas is discharged, and the control chamber pressure of a control chamber (crank chamber) in which the swash plate is housed, while also opening and closing by being driven by electromagnetic force.
One such capacity control valve is known, which, as shown in FIG. 7, comprises: discharge-side passages 73, 77 connecting the discharge chamber and control chamber; a first valve chamber 82 formed midway along the discharge-side passages; intake-side passages 71, 72 connecting the intake chamber and control chamber; a second valve chamber (actuation chamber) 83 formed midway along the intake-side passages; a valve element 81 formed in such a way that a first valve 76 placed in the first valve chamber 82 to open and close the discharge-side passages 73, 77, and a second valve 75 placed in the second valve chamber 83 to open and close the intake-side passages 71, 72, undergo reciprocating motion in a unified manner while opening and closing in the opposite directions, respectively; a third valve chamber (capacity chamber) 84 formed midway along the intake-side passages 71, 72 near the control chamber; a pressure-sensitive body (bellows) 78 placed in the third valve chamber to apply a biasing force in the extending (expanding) direction while contracting as the ambient pressure increases; a valve seat body (engagement part) 80 provided at the free end of the pressure-sensitive body in the extending/contracting direction and having a ring-shaped seating surface; a third valve (valve-opening connection part) 79 that moves integrally with the valve element 81 in the third valve chamber 84 and is able to open and close the intake-side passages by engaging with and separating from the valve seat body 80; and a solenoid S, etc., that applies an electromagnetic drive force to the valve element 81 (hereinafter referred to as “prior art”; refer to Patent Literatures 1 and 2, for example).
Then, this capacity control valve 70 is such that, when a need arises to change the control chamber pressure, the pressure (control chamber pressure) Pc in the control chamber can be adjusted by connecting the discharge chamber and control chamber without having to provide the variable-capacity compressor with a clutch mechanism for capacity control. The valve is also constituted in such a way that, if the control chamber pressure Pc rises when the variable-capacity compressor is stopped, the third valve (valve-opening connection part) 79 is separated from the valve seat body (engagement part) 80 to open the intake-side passages, thereby connecting the intake chamber and control chamber.
Now, when the swash-plate type variable-capacity compressor is started after an extended period of non-operation, the set discharge rate cannot be ensured through compression of refrigerant gas unless liquid refrigerant (refrigerant gas that has cooled and liquefied during the non-operational period) collected in the control chamber (crank chamber) is discharged.
So that desired capacity control is implemented immediately after the startup, liquid refrigerant in the control chamber (crank chamber) must be discharged as soon as possible.
With the capacity control valve 70 based on the prior art, first of all, liquid refrigerant collects in the control chamber (crank chamber) of the variable-capacity compressor if the variable-capacity compressor remains non-operational for an extended period of time with the solenoid S turned off and the connection passages (intake-side passages) 71, 72 blocked by the second valve 75. If the variable-capacity compressor remains non-operational longer, pressure equalization occurs inside the variable-capacity compressor and the control chamber pressure Pc becomes much higher than the control chamber pressure Pc and intake chamber pressure Ps when the variable-capacity compressor is being driven.
If the solenoid S is turned on and valve element 81 begins to start in this state, the first valve 76 moves in the valve-closing direction simultaneously as the second valve 75 moves in the valve-opening direction, while liquid refrigerant in the control chamber of the variable-capacity compressor is discharged. Then, the control chamber pressure Pc causes the pressure-sensitive body 78 to contract and the third valve 79 to separate from the valve seat body 80 and open. Here, because the second valve 75 is open and thus the connection passages (intake-side passages) 72, 71 are open, liquid refrigerant in the control chamber is discharged to the intake chamber of the variable-capacity compressor through the connection passages (intake-side passages) 74, 72, 71. Then, when the control chamber pressure Pc drops to the specified level or lower, the pressure-sensitive body 78 restores itself elastically and extends, and the valve seat body 80 engages with the third valve 79 and closes, thereby causing the connection passages (intake-side passages) 74, 72, 71 to be blocked.
However, the prior art is based on a complex structure having the valve seat body (engagement part) 80 provided at the free end of the pressure-sensitive body 78 in the extending/contracting direction and having a ring-shaped seating surface, as well as the third valve (valve-opening connection part) 79 that moves integrally with the valve element 81 in the third valve chamber 84 and is able to open and close the intake-side passages by engaging with and separating from the valve seat body 80, and there is also a limit to how much the discharge of liquid refrigerant can be improved further partly because changing the bore of the third valve 79 is not easy and partly because the liquid-refrigerant discharge flow passages have many windings and turns and are also long and therefore subject to high discharge resistance.